The present invention relates to a method for regeneration of molybdenum-containing oxide fluidized bed catalysts deteriorated in activity which have been used for ammoxidation reaction of propylene.
It is known to use molybdenum-containing oxide catalysts for ammoxidation reaction of propylene, and, as examples thereof, mention may be made of molybdenum-bismuth-containing catalysts disclosed in U.S. Pat. No. 2,904,580, molybdenum.bismuth.iron-containing catalysts disclosed in U.S. Pat. No. 3,226,422, catalysts containing molybdenum.bismuth.iron.cobalt.nickel, etc. disclosed in GB-A-1,319,190, and catalysts containing further multiple components disclosed in U.S. Pat. Nos. 5,132,269, 5,134,105 and 5,663,113. However, it is known that these catalysts sometimes deteriorate in activity owing to use in long-term reaction or setting of improper reaction conditions.
Various attempts have been made on regeneration of catalysts deteriorated in activity due to the use in reactions. For example, U.S. Pat. No. 4,425,255 proposes a method which comprises heat treating a deteriorated molybdenum-containing catalyst at 200-700xc2x0 C. in a reducing gas and then calcining the catalyst at 500-700xc2x0 C. in an oxygen-containing gas; U.S. Pat. No. 4,052,332 discloses a method which comprises impregnating a deteriorated K.Co.Ni.Fe.Bi.P.Mo-containing catalyst with Bi.Mo components and calcining the resulting catalyst; and U.S. Pat. No. 4,609,635 discloses a method which comprises impregnating a deteriorated catalyst containing Mo.Bi.P.Fe.Co.Ni-alkali metal with an aqueous molybdate solution, drying the resulting catalyst and then calcining the catalyst at 250-450xc2x0 C. However, these proposed methods are complicated in regeneration operation and insufficient in recovery of the catalyst performance, and, thus, still have many problems to be solved. These are industrially important tasks to be solved.
The present invention provides a method of effective reactivation of molybdenum-containing oxide catalysts deteriorated in activity due to being used in reactions, which has been an industrial important task to be solved as mentioned above.
As a result of an intensive research conducted by the inventors in an attempt to solve the above problems, it has been found that when a deteriorated catalyst is impregnated with a solution of a molybdenum compound and a solution of a compound of a specific element or a mixture of these solutions, and the resulting catalyst is dried and then calcined at a specific temperature, the catalyst performance is improved to a performance equal to or higher than that of a fresh catalyst. Thus, the present invention has been accomplished.
That is, the present invention relates to a method for regeneration of a molybdenum-containing oxide fluidized bed catalyst which comprises impregnating a fluidized bed catalyst of a metal oxide containing molybdenum, bismuth and iron which has been deteriorated due to being used for a reaction in production of acrylonitrile by ammoxidation of propylene, with a solution of a molybdenum compound and a solution of at least one compound containing at least one element selected from the group consisting of iron, chromium, lanthanum and cerium which are prepared separately or with a previously prepared mixed solution of the above compounds, drying the resulting catalyst and, then, calcining the catalyst at a temperature of 500-700xc2x0 C.
The molybdenum-containing oxide catalysts for fluidized bed to which the method of the present invention can be applied are catalysts containing molybdenum, bismuth and iron which have been deteriorated due to being used for reactions.
The method of the present invention is particularly effective for regeneration or reactivation of oxide catalysts for fluidized bed which have the following composition.
Mo10BiaFebSbcDdEeFfGgHhOi (SiO2)j
In the above formula, Mo, Bi, Fe and Sb represent molybdenum, bismuth, iron and antimony, respectively, D represents at least one element selected from the group consisting of magnesium, calcium, strontium, barium, chromium, manganese, cobalt, nickel and zinc, E represents at least one element selected from the group consisting of copper, silver, cadmium, aluminum, gallium, indium, germanium, tin, lead, titanium, zirconium and hafnium, F represents at least one element selected from the group consisting of vanadium, niobium, tantalum, tungsten, yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, thorium, uranium, rhenium, ruthenium, osmium, rhodium, iridium, palladium, platinum and gold, G represents at least one element selected from the group consisting of phosphorus, boron and tellurium, H represents at least one element selected from the group consisting of lithium, sodium, potassium, rubidium and cesium, O represents oxygen and Si represents silicon, the suffixes a, b, c, d, e, f, g, h, i and j represent an atomic ratio, and in the case of Mo=10, a=0.1-5, b=0.1-15, c=0-20, d=0-10, e=0-10, f=0-5, g=0-5, h=0-3, i is the number of oxygen corresponding to an oxide produced by bonding of the above respective components, and j=20-150.
It is preferred that the catalyst before subjected to regeneration (deteriorated catalyst), the catalyst after subjected to regeneration by the method of the present invention and the catalyst just after preparation are all in the range of the above composition.
The regeneration treatment of the deteriorated catalyst according to the present invention is carried out by impregnating the catalyst separately or simultaneously with a solution containing the molybdenum component and at least one solution containing at least one element selected from iron, chromium, lanthanum and cerium which are individually prepared or with a previously prepared mixed solution of them and, then, calcining the resulting catalyst. If necessary, the impregnation can be carried out in parts in a plurality of times. It has been found that such regeneration treatment can modify the deteriorated catalysts into catalysts having a performance superior to that of fresh catalysts.
When the catalyst is impregnated with molybdenum and other components, the composition of the impregnation elements in atomic ratio is Mo1AaBbCc wherein A is at least one element selected from the group consisting of phosphorus, boron, tellurium and bismuth, B is at least one element selected from the group consisting of iron, chromium zirconium, lanthanum and cerium, and C is at least one element selected from the group consisting of magnesium, manganese, nickel and cobalt, a=0-1, b=0.03-1, preferably b=0.05-0.8 and c=0-1, and molybdenum to be impregnated is 0.01-2 in atomic ratio when molybdenum in the catalyst is assumed to be 10 in atomic ratio. If amounts of the impregnation components exceed the above range, this is not preferred from the activity of the catalyst because yield of the desired product decreases. Especially, when the amount of the molybdenum component is large, deterioration in properties is also caused, for example, sticking, solidification or the like occurs at the time of preparation of the catalyst or molybdenum scale is generated at the reaction. In the case of impregnation with molybdenum alone, both the selectivity and the reaction rate are not sufficiently improved. In the case of addition of only the B component, rather, decrease of selectivity and reduction of reaction rate are caused. It is considered. that by the addition of both the molybdenum and the B component, the synergistic effect in improvement of performance is exhibited. If the ratio of the B component to molybdenum is less than 0.03 (atomic ratio), recovery or development of the catalytic performance is insufficient, and if it exceeds 1, deterioration of the catalytic performance is caused, for example, yield of the desired product rather decreases. The A and C components are added depending on the purpose, such as for control of reaction rate or inhibition of production of by-products.
To the impregnating solution in the method of the present invention, if necessary, there may be added in a small amount other components than molybdenum and the A, B and C components, such as sodium, potassium, rubidium, cesium, yttrium, praseodymium, neodymium, samarium, vanadium, niobium, tungsten, copper, silver, and zinc.
As starting materials used for preparation of the impregnating solutions in the method of the present invention, there may be used ammonium molybdate, peroxymolybdic acid and/or an ammonium salt thereof, phosphorusmolybdic acid, silicomolybdic acid, etc. as the starting materials for the molybdenum component. Especially, peroxymolybdic acid and/or a salt thereof which are prepared from molybdic acid or a salt thereof and hydrogen peroxide produce stable mixed solutions with many compounds and therefore use of them is convenient. If it is difficult to prepare a stable mixed solution, solutions of the compounds of the respective component elements are prepared and the impregnation operation may be successively repeated using them.
As the starting materials for the A, B and C components, it is convenient to use water-soluble compounds such as orthophosphoric acid for phosphorus, boric acid for boron, and telluric acid for tellurium, and nitrates of bismuth, iron, chromium, zirconium and cerium for bismuth, iron, chromium, zirconium and cerium. As for magnesium, manganese, nickel and cobalt, it is also convenient to use nitrates thereof. These are dissolved in water and amount of the solutions is adjusted to obtain impregnating solutions.
In impregnation, the pore volume of the deteriorated catalyst is previously measured, and an impregnating solution in an amount of 80-110%, preferably 90-98% of the pore volume is prepared in which are dissolved a given amount of a starting compound for molybdenum and a given amount of a starting compound for the B component or, if necessary, a starting compounds for the A and/or C components. Then, the solution was pored to the deteriorated catalyst, followed by well mixing. After completion of the impregnation, the catalyst is dried and calcined.
The calcination is carried out preferably under movement of the catalyst particles. For calcination it is suitable to employ a rotary calciner, a fluidized bed calciner, etc. If the catalyst is calcined with being fixed, it sets and results in inconvenience for use as a fluidized bed catalyst or its activity is not sufficiently developed. Especially preferably, a fluidized bed calciner which can more severely perform the control of calcination temperature is used at the final firing.
Atmosphere in calcining is usually air, but in addition there may be used inert gases such as nitrogen, carbon dioxide and water vapor or reducing gases such as various oxygen-containing gases containing ammonia, organic compounds or the like.